A fundamental property of a sample, whether it is a gas, liquid or solid, is its tendency or lack of tendency to absorb or scatter light at certain wavelengths. Characterization of the tendency of a sample to absorb, scatter or transmit is the basis for many optical measurements and instrumentation (e.g., spectrophotometry). The accuracy and repeatability of measurements taken with optical devices relates to many factors, including the strength of signal reaching one or more detectors. Optical devices may be used to measure the presence and quantities of components in human or animal blood or interstitial fluid. In one example, a non-invasive optical apparatus may use some form of spectroscopy to acquire the signal or spectrum from a target area of a body of the user.
The American Diabetes Association reports that over six percent (6%) of Americans, more than 17 million people, have diabetes. According to scientists with the Centers for Disease Control (“CDC”), one in three children born in the United States in year 2000 will become diabetic unless many more people start eating less and exercising more. One CDC study revealed that there were approximately 11 million diagnosed cases of diabetes in 2000 and that the number of diagnosed cases could rise to 29 million by the year 2050.
A vital element of diabetes management is the self-monitoring of blood glucose concentration by diabetics in the home environment. However, current monitoring techniques discourage regular use due to the inconvenient and painful nature of drawing blood or interstitial fluid through the skin prior to analysis. As a result, non-invasive measurement of glucose concentration is a desirable and beneficial development for the management of diabetes.
There exist a number of non-invasive approaches for blood glucose determination. One technique of non-invasive blood chemicals detection involves collecting and analyzing light spectra data. Extracting information about blood characteristics such as glucose concentration from spectral or other data obtained from spectroscopy is a complex problem due to the presence of components (e.g., skin, fat, muscle, bone, interstitial fluid) other than blood in the area that is being sensed. Such other components can influence these signals in such a way as to alter the reading. In particular, the resulting signal may be much larger in magnitude than the portion of the signal that corresponds to blood, and therefore limits the ability to accurately extract blood characteristics information.